Fast-Track Vapor Intrusion Assessments Using HAPSITE Portable GC-MS

Transcription

1 Fast-Track Vapor Intrusion Assessments Using HAPSITE Portable GC-MS Presented by: David Shea, P.E. Sanborn, Head & Associates, Inc. May 30, 2014 Building Trust. Engineering Success.

2 Presentation Goal: to show how real-time field analytical capability can fast-track VI investigations, data interpretation, and mitigation. Presentation topics: Overview of portable GC-MS (HAPSITE ) Project examples Baseline indoor air assessment HVAC experiments to distinguish VI from interior VOC sources Sleuthing for VOC entry pathways Avoid sub-slab sampling Comparability of field data with conventional samples (TO-15) Cost comparisons: conventional vs. real-time assessment 2

3 Portable gas chromatograph-mass spectrometer (GC-MS) Hazardous Air Pollutants on-site: HAPSITE manufactured by INFICON, Syracuse, NY Instrument can detect a wide range of chemicals at the low ug/m 3 level Boiling point < 250 C (~ 482 F) Molecular weight < 300 Mass fragments between 41 and 300 atomic mass units Portable at ~35 lbs Battery (2-3 hrs) or AC powered Air samples drawn into the instrument through the probe Typically 6-10 minutes from sample collection to result Can also be run in survey mode - continuous screening for compound ID and general magnitude assessment instant results 3

4 Project Example: PCE and TCE in indoor air in former mill building converted to apartments Is it VI or art supplies? 4

5 Analyzed ~80 samples over 2 days in 25 apartments Analyzed household products, art supplies, and potential VI pathways Hapsite set up on mobile cart in laundry room Sniffing for VI from cracks under rugs Rugs over original concrete floor slab Results: PCE due to art supplies. TCE due to VI through floor cracks. 5

6 Background VOCs (a.k.a. other sources) VI contaminants of interest are commonly found in consumer products and building materials Presence in indoor air is not necessarily related to vapor intrusion Discerning the source of VOCs can be difficult Possible sources: Current, past chemical use/storage Former use (residual mass) Building materials, fabric treatments Ambient, outdoor air Vapor intrusion 6

7 Collecting an ambient (outside) air sample to establish background conditions 7

8 Sample location IDs Response of indoor VOC levels to change in room pressure: negative pressure = higher VOC levels Results indicate VI rather than interior VOC source. 8

9 Sample location IDs Summa TO-15 sample results show order-of-magnitude agreement 9

10 In 1 day of real-time assessment: Obtained and analyzed 27 samples using the HAPSITE GC-MS Established baseline indoor air VOC conditions Without sub-slab sampling, confirmed that baseline conditions were due to vapor intrusion, not interior sources Identified the vapor entry pathways (i.e. the expansion joints), which suggested a remedial solution (re-caulking/sealing the joints) 10

11 Hypothetical Cost Comparison*: VI assessment of 20,000 sq ft building * Cost estimates are for relative comparison and do not include other items likely common to both approaches, such as report preparation, project management, and QA/QC 11

12 In 2 days of real-time assessment: Obtained and analyzed ~75 samples using the HAPSITE Established baseline indoor air VOC conditions throughout the bldg Confirmed that baseline conditions were due to vapor intrusion, not indoor sources Identified the vapor entry pathways to inform mitigation 12

13 Hypothetical Cost Comparison*: VI assessment of 100,000 sq ft building * Cost estimates are for relative comparison and do not include other items likely common to both approaches, such as report preparation, project management, and QA/QC 13

14 Summary: Rapid, effective VI investigations can be conducted using real-time analytical instruments (e.g. HAPSITE portable GC-MS), understanding of HVAC system operations and influence, and good detective work. Real-time analytical capability allows for: experimentation (e.g. induce positive or negative pressure) to distinguish VI vs. interior VOC sources/ background conditions, and possibly avoid sub-slab sampling. Trial testing of mitigation and effectiveness (e.g., increased pressure, air exchange, sealing penetrations) before committing long-term resources. Large potential cost savings compared to conventional, iterative investigations and sampling methods (e.g., Summa TO-15). Field data and lab data compare well, generally achieving order-of-magnitude agreement sufficient for relative assessments and identifying sources/pathways. May need enhanced QA/QC or conventional methods (e.g. TO-15) for samples intended to support final decisions (e.g., regulatory closure) 14

15 Upcoming Presentations: Vapor Intrusion, Remediation, and Site Closure Conference Cherry Hill, NJ, September 10-11, 2014 Conference on Soils, Sediments, Water, and Energy UMass-Amherst, October 20-23, 2014 Further reading/references: Sanborn Head technical papers available at: Any questions, please contact: David Shea, PE Sanborn, Head & Associates, Inc. Concord, NH (603)